1. Field of the Invention
This invention relates to an apparatus for testing devices.
More particularly, this invention relates to an apparatus for testing semiconductor devices.
In a further and more specific aspect, the present invention relates to an apparatus and method for testing semiconductor devices.
2. Prior Art
Integrated circuit devices, tiny electronic circuits used to perform a specific electronic function, are normally combined with other components to form a more complex system. Typical integrated circuits (IC's) are formed as a single unit by diffusing impurities into single-crystal silicone, which then serves as a semiconductor material, or by etching the silicone by means of electron beams. Several hundred identical integrated circuits are made at a time on a thin wafer several centimeters in diameter, and the wafer is subsequently sliced into individual ICs called chips. Chips are assembled into packages containing external electrical leads to facilitate insertion into printed circuit boards for interconnection with other circuits or components.
Integrated circuits have produced revolutionary changes in electronic equipment. Computer technology has benefited greatly. The logic and arithmetic functions of a small computer can now be performed on a single VLSI chip called a microprocessor, and the complete logic, arithmetic, and memory functions of a small computer can be packaged on a single printed circuit board, or even on a single chip.
In consumer electronics, IC's have made possible the development of many new products, including personal calculators and computers, digital watches, and video games. They have also been used to improve or lower the cost of many existing products, such as appliances, televisions, radios, and high-fidelity equipment. They have been applied in the automotive field for diagnostics and pollution control, and they are used extensively in industry, medicine, traffic control (both air and ground), environmental monitoring, and communications.
Due to the important role IC's play in industry, they need to be tested at various steps in the manufacturing or production process in order to evaluate their operation and quality. Many tests are carried out by passing voltage through the IC and checking to ensure set inputs yield desired outputs. Normally, IC devices are provided with external leads having various shape configurations such as gull-winged leads. Thus, a common method of testing an IC device is actuating the IC by engaging the external leads with a contact portion of a test socket. The contact portion of the test socket electronically communicates with a testing device facilitating the measuring of electrical outputs based on set electrical inputs. Typically, when the contact portion becomes engaged with the external leads to provide the metal to metal contact necessary for a proper electrical connection, it is referred to as an "insertion," "actuation," or "hit."
Test sockets are ideally suited for production test and device characterization. In production test, the extended life of the socket is important because it allows the cost of the socket to be amortized over the production of a large number of parts, and it reduces down time required to maintain or replace the sockets. Sockets used for production test are also called contactors to denote the extended life. For instance, the term "socket" is often used to describe devices which will handle anywhere from one to perhaps fifty insertions, actuations, or hits. A contactor or test socket, normally accommodates from 1,000 to 1,000,000 insertions.
In device characterization, superior electrical quality is important for determining how well an IC functions. Ideally, device characterization measurements reflect the part performance and need not be colored by the test environment, particularly the socket. Device characterization is typically performed using a "hand socket" having a lid mechanism attached to a socket housing.
Characteristics of sockets which determine their applicability to given test situations include reliable contact, electrical performance and mechanical performance. The two main factors which impact the ability of the socket to establish reliable contact are penetrating contaminants on the device leads and accommodating lack of lead coplanarity. During the manufacturing process, various contaminating elements build up on the lead of the IC, not the least of which is natural oxidation of the lead materials. When testing the parts, the contacting mechanism must break through these contaminants. The typical method of doing this is with a "wiping" connection in which the lead to be contacted slides past, and is gently abraded or cut into by the socket contact.
The second factor is lack of coplanarity. Ideally, all leads on a multi-lead part contact a flat surface. e.g., the contacts on a socket, at the same time. Typically, the three lowest leads define the plane of contact and all other leads will miss the surface. There are several root causes, namely, the differing thickness of the leads, differing alignments of the leads due to mishandling, presentation of the device to the socket at an angle, differing height or thickness of the socket contacts, and probably many others. The solution is for there to be compliance or flexibility somewhere in the system so that the device leads and the socket contacts can adjust themselves to mate properly.
Electrical performance, as mentioned above, is measured in terms of various parameters including, but not limited to, inductance and capacitance. The design elements in a socket which influence these parameters include lead length and lead form.
The mechanical performance of a test socket possesses an array of concerns or factors including the number of insertions, proper alignment of the device to be tested, lack of damage to the device, susceptibility of the socket to damage, and temperature ranges, etc. One component which influences many of these factors is the pitch or lead spacing of the devices being tested. As semiconductors have become more complex and powerful, the number of inputs and outputs to a single device has increased. Where twenty years ago a single chip would have perhaps 28 inputs/outputs maximum on 0.1" centers with substantial leads, today devices will have 400 or more and new package types are being designed with up to 1000. As a result, there are more leads which are finer and closer together. Today, parts with leads 0.007" wide with 0.008" space between them are being used. The impact of these scales on test sockets is twofold: there is very little tolerance for misaligning the part with the socket, and the leads are easily damaged.
The prior art has provided an array of apparatus for testing IC's or packaged semiconductors, and having impressive electrical and mechanical characteristics. In particular, existent in the prior art is a semiconductor chip test jig for testing primarily chips having "gull-wing" shaped leads. Provided is a body incorporating a cover having a pressure body that is hinged or gimbaled therewith, allowing limited horizontal mobility of the pressure body. Depending from the pressure body exist a set of "knife-edge" lead supports. When the cover is engaged with the body of the jig, bottom edges of the lead supports, which match the trim of the semiconductor chip leads, press against the leads of the semiconductor chip, which bring the leads into engagement with spring-loaded pins. Since the bottom edges of the lead supports match the trim of the semiconductor chip leads, the pressure body will not occasion deformation of the lead when pressure is applied thereto. Also, because the spring-loaded pins contact the leads at points directly opposite where they are supported by the pressure body, the pins will also not cause deformation of the leads. This apparatus is notable for testing devices having "gull-wing" shaped leads, and it seems to address the notions of coplanarity and compliance for achieving acceptable mechanical and electrical contact.
Also known in the prior art is a compliant pad apparatus including substrate suitably constructed of silicone or ceramic material. An interconnect layer is provided on the upper surface of the substrate, with a metal pad positioned intermediate the surface of the interconnect layer and a pad constructed of an electrically conductive, compliant material. At the upper surface of the electrically conductive compliant pad is a contact layer comprising a thin layer of conductive metal, against which the lead from the integrated circuit is received. Like the aforementioned apparatus, this apparatus introduces compliance or flexibility from the bottom of the lead, and seems to address the notion of coplanarity for achieving acceptable mechanical and electrical contact.
However, the inherent shortcoming of the above mentioned prior art devices, is that the compliance is provided from the contact surface of the test apparatus. Thus, the contact surface is provided as being inherently compliant or flexible. Also, as the leads of the device to be tested get smaller, flat rigid contact surfaces become necessary for achieving the desired mechanical and electrical connection. Additionally, since device leads are inherently non-coplanar due to mechanical variations resulting from manufacturing and mishandling, it is desirable to provide a device that functions as if the leads were coplanar. That is, it is desirable to have flat and rigid lead to contact engagement, otherwise known as coplanarity, in addition to compliance for absorbing the mechanical imperfections existent in the leads and the contact surface of the test apparatus.
In a more specific aspect, apparatus that introduce compliance from the contact surface, or bottom, of the leads of the device to be tested are inherently complicated mechanical devices which become increasingly more difficult to manufacture when the leads become increasingly small. Also, the mechanical mechanism required to introduce compliance from beneath the leads compromises the electrical connection of the test apparatus. Therefore, it seems desirable to provide an apparatus which can be used with devices having an array of lead sizes from the very small to the more larger, is inexpensive to manufacture, and that provides compliance with the use of flat rigid contact surfaces. Yet, it is imperative to have a non-compliant contact surface for achieving superior contacting between the leads of the device to be tested, and the contact surface.
Another pertinent apparatus includes a resilient probe device for use in electrically testing printed circuit boards, and used in place of conventional metal test pins. Specifically provided is an elongate strip of non-conductive elastomeric material retained within a vertical slot formed in a rigid, non-conductive, preferably tapered holder, the elastomeric strip preferably extending therefrom. Imbedded within the interior of the elastomeric strip exist a series of vertically extending electrically conductive strip members projecting slightly beyond the elastomeric strip. The upper end of the holder is coupled to the under side of a topology circuit board. The elastomeric strip is compressed between the topology circuit board and a printed circuit board to establish electrical contact between test contact points via the imbedded conductor members. Like the above mentioned prior art devices, this apparatus introduces compliance or flexibility from the bottom of the lead, and seems to address the notion of coplanarity for achieving acceptable mechanical and electrical contact. However, as has herein been discussed, the non-compliant nature of the contact surface of this device is inherently impractical when the leads of the device to be tested become very small.
Other notable apparatus incorporate a lead backer which introduces force on the top of the leads for exerting the leads against a contact mechanism. However, these lead-backer systems are inherently non-compliant and do not yield satisfactory test results with non-compliant contacts.
Accordingly, the notable deficiencies inherent in the prior art rest upon the failure to provide a test socket that is mechanically efficient, and that occasions superior electrical contact with rigid contacts. In other words, the prior art has failed to provide a system that is both compliant for absorbing the mechanical variations inherent in the leads and the contact surface, and able to achieve substantial coplanarity between the leads and the contact surface for facilitating a superior electrical connection. Additionally, the above mentioned prior art devices each do not have appreciable extended life due to damaged occasioned to the contacts over a relatively small amount of actuations, and damage to the leads as a result of the failure to provide sufficient compliance.
It would be highly advantageous, therefore, to remedy the foregoing and other deficiencies inherent in the prior art.
Accordingly, it is an object of the present invention to provide a new and useful apparatus for testing semiconductor devices.
Another object of the present invention is to provide a new and useful apparatus that is easy and inexpensive to manufacture.
And another object of the present invention is to provide an apparatus that may be used without modification to existing technology.
Still another object of the present invention is to provide an apparatus having reliable and exemplary contact performance.
Yet another object of the instant invention is to provide an apparatus having superior electrical and mechanical performance.
Yet still another object of the instant invention is to provide an apparatus that may be used without causing damage to the device being tested.
And a further object of the invention is to provide an apparatus having an improved extended life.
Still a further object of the immediate invention is to provide an apparatus for introducing compliance in a systems having non-compliant contacts.
Yet a further object of the invention is to provide an apparatus able to attain substantial coplanarity between leads and a contact surface without causing damage to either the leads or the contact surface.
And still a further object of the invention is to provide an apparatus able to accommodate a wide range of mechanical variances inherent in leads of packaged semiconductor devices and in contact surfaces.
Another object of the instant invention is to provide an apparatus that improves the utility of the Particle Interconnect.RTM. contact substrate in test applications.
And another object of the instant invention is to provide an apparatus which is easy to use.
And yet another object of the instant invention is to provide an apparatus that may be used not only in hand held test applications, but also with automated testing apparatus.
And yet still another object of the instant invention is to provide a new and useful method for testing a device.